I think group therapy is a good idea. I'm socially avoidant, though not as severely as you're describing. Still, it's caused me a lot of pain. I was in a "partial hospitalization program," which I attended for a few months. My peers in the program helped me to connect with them more than I normally did with other people. I learned a lot from them.

Beyond your therapy, I would encourage you to practice doing things that feel uncomfortable. I used to dislike even going into a store to buy something. I pretty much got over that. People are more accepting than I gave them credit for. When I do encounter someone who is not in a good mood, I remind myself that it may have nothing to do with me.